In a conventional display device, the backlight module generally includes a light source and a reflection sheet, a light guide plate, a lower diffusion sheet, a lower prism sheet, an upper prism sheet, an upper diffusion sheet (or brightness enhancement film) which are sequentially disposed upwardly. The light guide plate is an essential element in the backlight module for guiding a light beam to a display panel. Specifically, when the light beam emitted from the light sources enters into the light guide plate, the light beam is guided to transmit to another end of the light guide plate by the principle of total reflection; this time the light beam will only be transmitted in the light guide plate and cannot emit out from the light exit surface of the light guide plate. In order to guide the light beam to emit out from the light exit surface of the light guide plate, microstructures are disposed on the bottom surface of the light guide plate. When the light beam is transmitted to the bottom surface of the light guide plate and touches the microstructures, the light beam is reflected by the microstructures and diffused at various angles, thereby destroying the total reflection condition and interference to emit the light beam out from the light exit surface of the light guide plate.
However, after the light beam emitted from the light source enters into the light guide plate and emits out from the light guide plate, the light beam will be repeatedly reflected between the prism sheet and the reflection sheet. The larger the number of times of the light beam reflection between the prism sheet and the reflective sheet is, the more serious the energy attenuation of the light beam is, which may lead to the overall decline in illumination. Specifically, when the light beam passes through the bottom surface of the light guide plate, the reflection light beam reflected by the reflection sheet is transmitted back to the light guide plate and emitted to the lower prism sheet through the light exit surface of the light guide plate. If the angle of the reflection light beam cannot match with the light-exiting angle of the lower prism sheet, then the reflection light beam will be reflected back to the light guide plate, and repeatedly, the light energy consumption will increase. Generally, in order to improve the illumination, in addition to disposing the microstructures with different density or different shapes on the light guide plate, the number of light sources or the current of the light source may be increased, however, the effect of the improvement is limited and the cost also increases. Therefore, how to reduce the number of times of reflection of light beam between the prism sheet and the reflection sheet to improve the above-mentioned problem and to effectively guide the light beam to emit out from the prism sheet is a focus of attention of those skilled in the art.
The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art.